Lake Speed Jr. is a self-described motor oil geek. He’s actually a pretty interesting guy: he’s held (big breath in here) Society of Tribologists and Lubrication Engineers Lubrication Specialist and Oil Monitoring Analyst certifications for a decade-plus. He also happens to be former NASCAR driver Lake Speed’s son. Lastly, he’s the grandson of late Mississipi mayor Leland Speed. In any case, the last name “Speed” sure seems appropriate for the family’s automotive passions. Anyway, Lake, who posts explainer videos on his YouTube channel The Motor Oil Geek, has a great video on the accuracy of oil life indicators.

How does an oil life monitoring system work?

Despite what most drivers might think, there isn’t a special sensor on cars that physically tests engine oil and determines it remaining “life.”

Instead, modern vehicle computer software has a high-level algorithm installed after three GM engineers came up with it…in the 1980s. It all originally came from Cadillac and Corvettes fitted with OnStar systems some 40 years ago.

The system collects data based on engine behavior, like cycle length, fuel injector fires, water temperature, and so on. From this data, the computer can actually predict engine oil wear.

The science behind oil wear gets very technical, but one of the bottom-line ideas is this: the more fuel forced into firing cylinders over time, the more it contaminates the oil. This contamination shortens the engine oil’s “life,” or its free space to suspend pesky contaminants.

This is why certain lubricated systems, like transmissions, can go tens of thousands of miles farther without a fluid change. Those systems don’t experience the fuel contamination vehicle engines face.

There are other factors at play, of course, like average temp during each engine cycle. All told, oil life indicators are designed to account for many contaminant rate variables.

If you take anything away from this intro lesson, know this: short, cold trips are devastating to engine oil life.

How accurate are oil life indicators?

Tribology is Speed’s specialty. It’s the study of friction, wear, and lubrication, and Speed is giddily obsessed. He uses a Cadillac to show an oil life indicator stating the lubricant only has 9% remaining. Speed decided to pop the hood and take an oil sample for analysis.

The car’s oil was last changed between 5,000 and 6,000 miles back.

While the correct-spec oil was used, the oil life indicator seems way, way conservative.

The test results say the oil sample has an oxidation rate of 13.2. For a Dexos oil, Speed says, this isn’t even close to nearing the end of the oil’s lifespan.

Speed thinks automakers err on the side of drivers needing some time once they’re told the engine life is low.

Now, he can’t speak for all oil life indicators. But, in the end, Speed says that any GM with the same oil life indicator as his tester can at least trust the system, and not worry whether the algorithm is underestimating oil life.